Immune responses can be elicited to tumor-expressed antigens. For example, several groups have reported the detection of antibody responses to prostate tumor-associated antigens compared with control groups (Wang X, et al., N. Engl. J. Med. 353:1224-1235 (2005); McNeel D, et al., J. Urol. 164:1825-1829 (2000); Minelli A, et al., Anticancer Res. 25:4399-4402 (2005); Bradford T, et al., Urol Oncol. 24:237-242 (2006); and Shi F, et al., Prostate 63:252-258 (2005)). Cancer-testis antigens (CTA) are of particular interest as potential tumor antigens given that their expression is typically restricted to germ cells among normal tissues, but aberrantly expressed in tumor cells (Scanlan M, et al., Cancer Immun. 4:1 (2004)). The absence of MHC class I molecule expression on germ cells makes CTA essentially tumor-specific antigens in terms of potential CD8+ T-cell target antigens (Kowalik I, et al., Andrologia. 21:237-243 (1989)). Many of these CTA were discovered using antibody screening methods including the serological evaluation of recombinant cDNA expression libraries (SEREX) approach (Sahin U, et al., Proc. Natl. Acad. Sci. USA 92:11810-11813 (1005); Hoeppner L, et al., Cancer Immun. 6:1-7 (2006); and Tureci O, et al., Mol. Med. Today 3:342-349 (1997)).
Several CTA, including members of the MAGE and GAGE families, have been identified as antigens recognized by tumor-specific cytotoxic T-cells (CTL) (Van der Bruggen P, et al., Science 254:1643-1647 (1991); and Van den Eynde B, et al., J. Exp. Med. 182:689-698 (1995)). Detectable immune responses to these antigens are believed to be a result of their ectopic expression in MHC class I-expressing malignant cells. Several CTA have been shown to be recognized by both antibodies and CTL, thus providing validation for the original approach of using antibody screening to identify potential tumor-specific T cell antigens (Jäger E, et al., J. Exp. Med. 187:265-270 (1998); and Monji M, et al., Clin. Cancer Res. 10:6047-6057 (2004)). Some CTA are expressed in several malignancies of different tissue origins (Scanlan et al., supra; and Mashino K, et al., Br. J. Cancer. 85:713-720 (2001)).